1. Field of the Invention
This invention relates to the field of micro-pumps used to forcedly cause sub-microliter amounts of fluid to flow in a predetermined flow pattern. Micro-pumps of this nature are used to circulate ink in print heads and could be used in other arenas such as in the medical field in which bodily fluid flow could be controlled during medical procedures or by medical intervention. More specifically, this invention relates to micro-pumps using a series of conductive elements, which are arranged in an array or in a matrix and are selectively and sequentially charged and discharged at a high frequency, to create a moving electromagnetic field which pulls charged fluid molecules in a predetermined direction.
2. Description of the Related Art
Some micro-pumps use a series of resistors with a similar design to that used in thermal ink jets. These pumps use a first resistor to evaporate fluid and thereby create a bubble that clogs a microchannel. Firing a second adjacent resistor forces the fluid to move away from the clogged channel section. An inherent disadvantage in this approach is that the evaporation of the fluid, to generate the necessary work, could cause a kogation (i.e., residue) to deposited on the resistors when the fluid in the device is repeatedly heated. The occurrence of a kogation is particularly possible when transporting fluids such as inks; as is well known in the art of inkjet printers a kogation of ink is deposited on thermal inkjet resistors when the ink is heated during millions of print cycles. Moreover, resistor life is impacted by the potential for cavitation of the bubbles collapsing and by the related thermal cycling they undergo. Furthermore, in the medical context, evaporation and/or heating of the fluid can present unacceptable treatment conditions, as the properties of the fluid are likely to change.
Another type of micro-pump uses electro-osmosis. With this type of pump, a large steady-state magnetic field is applied to one end of a fluid causing it to move due to the biased electric charge in each of the atoms in the fluid. This approach, however, does not provide for a predetermined fluid flow path, nor does it provide the ability to localize the magnetic field. In addition, the fluid flow generated through electro-osmosis is very slow as its movement is based solely on charge differentiation.
Accordingly, there is a need for a micro-pump which has one or more of the following features: (a) it is capable of creating a steady and defined fluid flow path which may be nonlinear; (b) it is capable of causing fluid to flow at a high velocity; (c) it is capable of creating the fluid flow path without causing the fluid to evaporate or to be heated; and (d) it is capable of causing the fluid to flow without the use of moving parts.
Among the embodiments of the micro-pump herein described, the first includes an array containing a plurality of conductive elements. A plate covers the array and a controller supplies and controls current to the conductive elements in the array. In this embodiment, the plate can be, and preferably is, a photopolymer. Moreover, if a photopolymer is used, it is preferable to use a thin-film photopolymer having a sub-millimeter thickness.
The conductive elements can have a current individually and sequentially applied therethrough or shut-off thereto by the controller. In addition, the controller operates to temporarily apply current to substantially all of the conductive elements in the array thereby enabling a fluid disposed on the plate to be separated into positively and negatively charged fluid molecules. Following this separation, the controller applies a current sequentially through selective of the conductive elements and shuts-off current thereto in a predetermined order to define a fluid flow path.
A fluid disposed on the plate and separated into positively and negatively charged molecules is forced to move along the fluid flow path by a moving electromagnetic field generated by the application of current and shutting-off of current to the selective of the conductive elements. Moreover, the fluid follows the direction of the moving electromagnetic field.
A second embodiment of a micro-pump includes a first array, containing a plurality of conductive elements, covered by a first plate. In addition, the micro-pump includes a second array, also containing a plurality of conductive elements, which is covered by a second plate. The first array is substantially parallel to the second array and the first and second plates are preferably photopolymers. Moreover, the first plate preferably abuts the second plate in such a fashion that microtubes are defined between therebetween.
The micro-pump also includes a controller which supplies and controls current to the conductive elements in the first and second arrays. In this embodiment, the conductive elements in the first and said second arrays can have a current individually and sequentially applied therethrough or shut-off thereto by the controller. Moreover, the current supplied to the second array is supplied in an opposite direction relative to the direction of the current supplied to the first array.
All of the conductive elements in the first and second arrays may have a current temporarily applied therethrough thereby enabling a fluid disposed between the arrays to be separated into positively and negatively charged fluid molecules. When selective of the conductive elements in the first and second arrays have a current sequentially applied thereto and shut-off thereto a fluid disposed between the arrays (and separated into positively and negatively charged molecules) is forced to move in a predetermined direction.
This invention also contemplates a method of generating fluid flow. The method involves creating, in a fluid, at least one working layer which contains a plurality of like-charged fluid molecules. An electromagnetic field encompassing the fluid is moved in a predetermined direction thereby creating at least one moving electromagnetic field; the moving electromagnetic field causes the fluid to move in the predetermined direction. In this method, the step of creating at least one working layer in a fluid includes applying (for a predetermined period of time) a current to a first array of elements to create a first steady electromagnetic field across the fluid and thereby a first working layer. Moreover, the step of moving the at least one steady electromagnetic field includes shutting-off the current to most of the first array elements and applying current to and shutting-off current to selected first array elements to create a first moving electromagnetic field.
Creating at least one working layer in a fluid may involve applying a current to a second array of elements to create a second steady electromagnetic field; the current applied to the second array preferably travels in a direction approximately opposite to the direction traveled by the current applied to the first array. Creating the at least one working layer may also involve applying the second steady electromagnetic field to the fluid to create a second working layer. The second array of elements is preferably substantially parallel to the first array of elements. In this fashion, the charge of the fluid molecules concentrated at the interface of the fluid and the second plate is the opposite of the charge of the fluid molecules concentrated at the interface of the fluid and the first plate.
Moving the electromagnetic field involves shutting-off the current to most of the second array elements and applying current to and shutting-off current to selected second array elements to create a second moving electromagnetic field. The application of current to and shutting-off current to select of the second array of elements occurs at substantially the same frequency as the step of applying current to and shutting-off current to select of the first array of elements. The first and the second moving electromagnetic fields move in substantially the same direction.
In this method, as fluid is moved through a microchannel or microtube, it may be replaced by new fluid. Accordingly, the method may involve replacing the fluid (which was moved in the direction of the at least one moving electromagnetic field) with new fluid. If the new fluid is to be moved, a current must be applied to some of the elements in the first array of elements to create a new steady electromagnetic field. The new steady electromagnetic field is applied to the new fluid to create at least one new working layer which contains a plurality of like-charged fluid molecules. Similar to the aforementioned steps regarding the original fluid, the current to those charged elements is shut-off and current is then cyclically applied to and shut-off to selected elements in the first array of elements to create a moving new electromagnetic field. The moving new electromagnetic field causes the charged new fluid molecules to flow in the direction of the moving new electromagnetic field.
A structural understanding of the aforementioned embodiments of the micro-pump as well as the method for generating fluid flow will be easier to appreciate when considering the detailed description in light of the figures hereafter described.